1. Field of the Invention
The invention relates to a directional microphone, more particularly to a directional microphone with superdirectional characteristics, which is simple and inexpensive to manufacture.
2. Description of the Related Art
A typical sound amplification system minimally requires a microphone, an amplifier and a loudspeaker for amplification and output of sounds. In operation, the microphone converts audio signals into electrical signals, which are amplified by the amplifier for transmission to the loudspeaker. The loudspeaker then converts the amplified signals into sounds for emission. In such a system, if the microphone does not have directional characteristics, it will pick up sound from all directions with equal sensitivity, which may create undesirable feedback that causes the loudspeaker to produce high-pitch noise. A directional microphone was developed in order to effectively suppress the feedback phenomenon.
The so-called directional microphone refers to one that has a notably low sensitivity with respect to sound from a particular direction. By virtue of the directional characteristics, sound from the particular direction can be suppressed to prevent feedback and hence high-pitch noise. For a unidirectional microphone, the sensitivity of the microphone is exceptionally low within a range of 180 degrees (the direction facing the microphone being 0 degree). Therefore, the unidirectional microphone is suitable for use on occasions in which the loudspeaker is disposed opposite to the user, and is not suitable for use on a stage as there will be serious feedback. There has been developed a type of superdirectional microphone that is especially adapted for use on a stage. During a live stage performance, the loudspeakers will not be arranged directly opposite the front of the stage, but will be disposed on both sides of the stage (forming a 120-degree directivity). Hence, the superdirectional microphone can reject sound signals from the 120-degree range and can hence suppress noise feedback.
FIGS. 1 and 2 show a microphone of the prior art. As illustrated, the microphone includes a protective cover 1, a sponge 101 disposed inside the protective cover 1, a voice coil 2, a diaphragm 3, a washer 4, a magnet 5, a yoke 6, an annular cap 7, and an air chamber unit 8. During manufacture, the washer 4, the magnet 5 and the yoke 6 are first assembled. The cap body 7 is formed integrally with the resulting assembly and simultaneously with a high-frequency resonance pad 701 as a plastic encapsulation by injection molding. The cap body 7 is also formed simultaneously with a plurality of through air chamber holes 702 and a plurality of lateral air holes 703. The air chamber holes 702 are pre-determined to be communicated with the air chamber unit 8. The lateral air holes 73 are communicated with radial air holes 704 in the lateral sides of the cap body 7. Next, the voice coil 2, the diaphragm 3, and the protective cover 1 are mounted in sequence on the front portion of the washer 4. Thereafter, an outer first sound regulating paper 9 is attached to surround the cap body 7 and the protective cover 1. Finally, after mounting a second sound regulating paper 901 onto the bottom portion of the cap body 7, the air chamber unit 8 is mounted at the bottom portion of the cap body 7 to complete assembly of the conventional microphone.
Although the above-described microphone can provide higher sensitivity and enhanced structural strength, it is a 180-degree directional microphone that is unsuited for specific occasions, for instance, on stage.
Therefore, the main object of the present invention is to provide a directional microphone with superdirectional characteristics, and which is simple and inexpensive to manufacture.
Accordingly, a directional microphone of this invention includes a yoke, a magnet, a washer, an annular cap body, a voice coil, a diaphragm, a protective cover, and an air chamber unit. The yoke has a surrounding wall portion with front and rear ends, and an end wall portion disposed to close the rear end of the surrounding wall portion. The magnet is disposed in the yoke, and has a front side and a rear side that lies against the end wall portion of the yoke. The washer is disposed in the yoke, and has a front side and a rear side that lies against the front side of the magnet. The cap body encloses the surrounding wall portion of the yoke, and has a front portion with a front end face, a rear portion with a rear end face, and a plurality of first and second air passages. The first air passages extend from the front end face through the rear end face and are angularly spaced apart from each other. The second air passages are formed in the front portion. Each of the second air passages has a radial first section that extends in a radial inward direction from an outer wall surface of the front portion, and an axial second section that extends from an innermost end of the first section to the front end face. The voice coil is disposed around the washer and the magnet within the surrounding wall portion of the yoke. The diaphragm is disposed adjacent to the front end face of the cap body, and has a peripheral portion connected to the voice coil. The protective cover includes a perforated cover plate and an annular surrounding wall. The annular surrounding wall extends from a periphery of the cover plate, and is coupled to the front portion of the cap body without covering the first sections of the second air passages and with the cover plate disposed proximate to the diaphragm. The air chamber unit is coupled to the rear portion of the cap body and is in communication with the first air passages. The rear portion of the cap body has an outer wall surface formed with a guide groove unit and a plurality of recesses for inter-communicating the first sections of the second air passages and the guide groove unit.